The present invention is related to a launch system for launching a payload into earth orbit. More specifically, the present invention is directed at an improved payload launch system which will optimize the use of existing technology, minimize the cost of placing payloads into orbit and substantially increase the number of possible launchings with minimum hardware to thereby make feasible a more rapid and comprehensive commercialization of space.
Previously contemplated systems for launching payloads into earth orbit can be classified into three classes; rocket technology, hypersonic flight technology, and hybrid rocket/airframe technology. Rocket technology, with rockets launching from the earth's surface, has to date been the primary technology used for launching payloads into earth orbit. The manned Mercury, Gemini, Apollo, and Space Shuttle programs all utilize such rocket technology. Such rocket technology also includes unmanned launch systems using Titan, Atlas, Delta, and other rocket assemblies. Hypersonic flight technology has been proposed, but not yet practically utilized, which would utilize an aircraft that would fly from the earth's surface directly into earth orbit and back to earth, utilizing a combination of air breathing jet engines and rocket engines. The so-called hybrid technology includes the B-52 launch of Pegasus rockets and other proposals such as the Sanger project, wherein an aircraft is used to lift a rocket to altitude, and then the rocket is launched from the aircraft.
Disadvantages of existing rocket technologies include (i) a high cost per pound of payload launched, especially for small and intermediate payloads up to 15,000 pounds; (ii) the consequent high investment risk factor due to the need to launch heavy payloads to reduce launch costs per pound of payload; (iii) the amount of hardware which is lost for each launch, including the requirement for rebuilding or repairing of earth surface launch pads subsequent to each launch; and (iv) the backlog in the time from launch request to delivery on orbit due to need for launch pad repairing and use of large multi-stage rocket propulsion systems.
Hypersonic flight technology launch systems have been contemplated, but not yet developed for practical use. Further, although such systems may be available some years in the future, there are many unanswered development questions which will likely require considerable expenditure of time and money to solve.
The hybrid technology which has been proposed, and to some extent utilized for example with the B-52/Pegasus system, is an attempt to combine flight dynamics with rocket dynamics. U.S. Pat. Nos. 4,265,416 and 4,802,639 disclose proposals for such hybrid technology launched systems.
The present invention is directed at providing an improved launch system utilizing hybrid technology which:
(a) improves cost effectiveness by maximizing hardware reuse; PA1 (b) maximizes the payload to be launched by optimizing the use of multiple propulsion sources, including use of aerodynamic lift and air breathing propulsion in the atmospheric stages of launch mission and use of rocket technology only when air breathing propulsion systems become impractical because of the altitude; PA1 (c) utilizes existing technology and hardware elements to the maximum extent; PA1 (d) minimizes atmospheric pollution; PA1 (e) is capable to support both large space platform construction programs and economical transportation for more routine intermediate payload telecommunications platforms; PA1 (f) minimizes acoustic and vibration loadings on the payload during launch operations; and PA1 (g) provides multiple launch site flexibility and improved scheduling efficiency.
According to one aspect of the present invention, a system and a method of launching a payload into earth orbit is provided which utilizes an airframe capable of flight from the earth's surface to an upper atmospheric launch altitude and velocity, the airframe platform carrying a payload launching rocket. In order to optimize the payload carrying capacity of the airframe launch platform, the fuel tanks for the air breathing jet engines which propel the airframe from take-off to an initial altitude are intentionally only partially filled to facilitate this first stage of the mission. Once the launch platform reaches the first altitude, an air refueling operation takes place which replenishes the fuel used in reaching that altitude and fills the fuel tanks with that portion of the fuel which was not included at take-off, taking advantage of the improved load carrying capacity at refueling altitude and velocity as compared to the ground take-off lifting weight. Utilizing this approach, the present invention can accommodate a much heavier payload launching rocket/payload than would be the case with a full fuel load at take-off.
According to another aspect of the invention, a payload launching rocket carried to launch altitude by an airframe is fueled by a mixture of liquid oxygen (LOX) and hydrogen. To minimize the earth surface lift-off weight and frontal profile of the combined airframe and payload launching rocket, and consequently allow for efficient airframe designs to optimize launch velocity and altitude of the airframe at launch of the payload launching rocket, the LOX tanks are left empty or only partially filled on the ground. An airborne filling of the LOX tanks is then carried out once the airframe is airborne and flying at a mid-level atmospheric altitude of about 32,000 feet. Since the LOX is relatively inert and easy to handle, this at altitude transfer of LOX to the launching rocket will be relatively safe and efficient to perform, utilizing existing mid-air refueling techniques. The mid-level altitude filling of the LOX tanks will also minimize problems of frost build-up and ventilation problems that would be present at ground level, because of the 32,000 foot altitude temperature and air density are less likely to experience such problems. Embodiments are also contemplated for mid-air fueling of other liquid/gaseous rocket fuel for the airframe rockets and/or the payload launching rocket.
According to preferred embodiments of the invention, the intentional minimization of both jet engine fuel and rocket fuel for the payload launching rocket at earth surface take-off, followed by airborne fueling and fuel replenishment at the mid-level altitude, can be combined to minimize lift-off weight and optimize resultant velocity of the assembly at launch altitude to thereby maximize the payload that can be placed in orbit and minimize the energy (fuel) costs for a payload launch.
Preferred embodiments of the present invention use air breathing jet engines for propelling the launch platform from the earth surface to a first refueling altitude of about 32,000 feet. After refueling, during the next flight phase to an altitude of about 75,000 feet, the jet engines are supplemented by mid-plane rocket motors between about 48,000 feet to 75,000 feet at which time the jet engines are shut down. At about 80,000 feet the main airframe rocket engine assembly is actuated to propel the airframe to 156,000 feet and slightly higher. At about 156,000 feet the airframe has a velocity about Mach 3.8. At this point, the airframe will be at an optimum launch altitude and velocity in an atmospheric regime for optimum rocket engine performance, at which time the payload launching rocket is separated from the airframe to place the payload into low earth orbit at a speed of Mach 25. The airframe is then piloted back to earth, utilizing its air breathing turbojet propulsion once it returns to lower atmospheric altitudes. In especially preferred embodiments of the invention, it is necessary to only use a single stage rocket as the payload launching rocket.
According to another advantageous aspect of preferred embodiments of the present invention, the payload launching rocket is also reusable and includes aerodynamic guide surfaces and a parachute assembly to facilitate a return soft landing on earth. In certain preferred embodiments, the payload launching rocket is provided with movable wings which are concealed during launch and deployable for the return soft landing. In other embodiments, small fixed wings can be provided.
The present invention is optimally designed for use in launching intermediate size payloads between 8,000 and 15,000 pounds.
Since the launching system of the present invention operates primarily at altitudes above 30,000 feet, most severe weather systems can be avoided with most of the flight occurring in blue sky, thereby improving on the flexibility of the launch system with respect to weather. With the exception of weather conditions that would ground conventional passenger airliners, such as hurricanes or fierce blizzards, the system is capable of facilitating a successful launch. Thus, maintaining launch schedules will be much more feasible than are the current rocket launch from earth surface system.
Since the disclosed preferred embodiment of the system of the present invention includes topping off of the jet engine fuel and rocket fuel transfer to the payload launching rocket at an altitude of about 32,000 feet at about 300 miles per hour, the airframe flight dynamics are optimized. In especially preferred embodiments, it is proposed that a LOX rocket fuel and jet engine fuel transfer would occur adding approximately 135,000 pounds to the airframe system, thereby allowing the airframe to be as small in aerodynamic cross-section as possible at take-off to facilitate higher rocket launch point velocities. This reduction in airframe cross-section lift-off weight is especially advantageous in permitting an airframe design that can reach the high altitude and velocities to facilitate a single stage payload rocket to then place a large payload into earth orbit.
The present invention advantageously implements a flight plan which can be segregated into three distinct regimes. The first flight segment is the airframe flight regime. This is the region where air breathing propulsion and aerodynamic flight systems operate well. This segment is from sea level to about 80,000 feet. In the upper portion of this first segment, rocket propulsion is used to assist the air breathing jet engines. Above 80,000 feet, both aerodynamic control and air breathing engine performance are dramatically reduced. The second flight segment is the airframe boost regime. This zone is from about 80,000 feet to the launch altitude of about 156,000 feet. In this second segment, rocket propulsion is also used to propel the airframe. The rocket propulsion efficiency at this altitude is much better than at sea level and can be further optimized. The airframe aerodynamic control systems do not contribute much after 125,000 feet, but the overall effectiveness of the winged vehicle easily justifies its existence. The third final flight segment, the rocket-only regime, is above 156,000 feet. Here the airframe main rocket motors are operational where this is the most efficient mode for these motors. Preferred embodiments of the system are sized to carry a 12,000 pound payload into low earth orbit, allowing the airframe to return to its place of origin, landing like a normal aircraft.
According to another aspect of preferred embodiments of the present invention, the structural loading at the time of launch of the payload launching rocket are minimized as compared to current rocket launch systems. This structural loading placed on the payload during a normal ground based rocket launch results from acoustic loads and random vibration loads combined with the acceleration loads during roll over. With the launch system of the present invention, there is no rocket roll over from the vertical launch altitude to a more horizontal orbit placement altitude because the payload rocket launch is from the airframe which is already flying substantially horizontally. The payloads must always be designed taking into consideration these loads. Once the payload is on orbit, the payload hardware normally sees little or no load and thus a reduction in launch loads facilitates a more economical design of the payloads. With the present invention, the acoustic launch loads are lower than for earth surface rocket launch because the rocket motors are ignited far away from any reflective surface such as the earth's surface. This contrasts with current rocket launch systems where the sound waves are reflected back to the rocket at lift-off before the rocket is moving fast enough to escape the sound waves. These acoustic loads will be minimal with the present invention since the launch is carried out from a platform that is at an altitude with minimal atmosphere for transmitting acoustic loads.
Further, random vibrations will be reduced by the present invention due to the fact that the magnitude of the energy impulses will be small relative to an equivalent ground launched first stage where the load is typically highest. Also, roll over is the part of the flight when a ground launched rocket turns from a vertical direction to something closer to horizontal relative to the earth's surface. This maneuver can sometimes place high loads on the payload. Again the system of the present invention does not go from vertical to horizontal in an abrupt manner so this "roll over" load case does not exist.
Another advantageous aspect of the system and method of the present invention is the design of the arrangement for separating the payload launching rocket from the airframe. According to preferred embodiments of the present invention, the impulse of the airframe is matched with the impulse of payload launching rocket booster and payload assembly during launch separation for a smooth and controlled separation. It is contemplated by the invention that neither of the components rapidly accelerate away from one another, but simply separate, accelerating together to a point where the total separation is sufficient enough to allow the airframe rocket to be throttle back or shut off while the payload launching rocket assembly accelerates onto orbit. This separation arrangement minimizes rocket plume effects on from the payload launching rocket on the airframe and from the airframe rockets on the payload launching rocket assembly, thereby resulting in a very smooth separation sequence.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.